When the NFL acted swiftly in March, with little to no advance warning, to put in place its new safety rule about a player lowering his head to deliver a hit with his helmet, league leaders hailed it as a major development with broad and significant implications for safeguarding players. But they also knew there would be considerable consternation surrounding the arduous process of actually putting the rule into effect.

They were oh-so-right about that.

One game into the NFLs preseason, some players and other observers remain highly skeptical and sharply critical of the implementation of the rule, which subjects a player to a 15-yard penalty and possible ejection, fine or suspension for lowering his head to use his helmet to hit an opponent. With the first full slate of preseason games coming this week, there is certain to be intense scrutiny of how the on-field officials are enforcing the new rule.

Weve always known on the competition committee that change is hard, Atlanta Falcons President Rich McKay, the chairman of that rulemaking committee, said in a phone interview. People are resistant to it. They dont know whats going to happen.

McKay compared the transition period that players, coaches, officials and fans now face with this rule to the gradual acceptance that followed the NFLs enactment of its first rules regarding illegal hits on defenseless players in the mid-1990s.

When we first put the defenseless player rules in, people said, Youve changed the game. This isnt football anymore. You wont see any hard hits ever again,  McKay said. But within two years, I didnt hear that much complaining. It became part of our game and part of how our game was taught. Im sure this will be like that. But I dont ever discount the fact that there will be an adjustment period for everyone.

The new rule was called twice during last weeks Hall of Fame Game in Canton, Ohio, between the Baltimore Ravens and Chicago Bears. Ravens linebacker Patrick Onwuasor was penalized about four and a half minutes into the game. Another Baltimore linebacker, Kamalei Correa, was called for a third-quarter penalty.

Both calls were made against defensive players in open-field situations. Both were fairly obvious violations. That may have provided an early hint as to how the rule will be enforced, although it potentially applies to all players on the field in a variety of situations – including a ball carrier lowering his head at the end of a run or an offensive lineman lowering his head to deliver a block.

The rule is so simply written but it expands so far, depending on how its applied, former NFL referee Terry McAulay, now a rules analyst for NBC, said at the end of the networks broadcast of last Thursdays game.

Still, there was confusion and controversy. There were two personal fouls called for illegal hits during the Ravens-Bears game not based on the new rule. Yet each one prompted a discussion of the helmet rule on the broadcast and on social media. Overall, many did not like what they saw.

I cannot emphasize enough how bad this rule is for the [NFL], agent Blake Baratz wrote on Twitter. They are literally ruining their game. It will be a complete disaster come the regular season.

Others hold similar views. Minnesota Vikings safety Andrew Sendejo has been spotted in training camp wearing a hat that says, Make Football Violent Again. Washington Redskins safety D.J. Swearinger greeted passage of the rule in March by writing on Twitter: THE GAME WE LOVE IS GETTING DESTROYED EVERYDAY[.]

But other players are more accepting.

Some of it is kind of tough because I feel like theyre taking a little bit of the aggressiveness out of the game, Houston Texans cornerback Aaron Colvin said last week at his teams training camp in White Sulphur Springs, West Virginia. But also, I can understand it because theyre trying to protect players as well. . . . Its kind of [like being between] a rock and a hard place, honestly.

The rule is enacted as the NFL continues to deal with issues related to concussions suffered by players and the possible long-term health consequences of brain injuries. NFL leaders said the new rule comes after data showed an increase in the percentage of players concussions that were being caused by helmet-to-helmet hits. The technique of lowering the head to deliver a hit, they say, is dangerous to both the player delivering the hit and the player receiving it. Pittsburgh Steelers linebacker Ryan Shazier suffered a serious spinal injury on a hit last season.

The goal, the NFL says, is to stop players from using their helmets as an on-field weapon. The new rule has been called the NFLs version of a college-style targeting rule. But its not a targeting rule, NFL leaders say. It is not based on the target of a hit being an opponents head. It is broader than that, being based on the technique of the player delivering the hit.

Its a safety thing, Texans cornerback Kevin Johnson said last week in West Virginia. I get it. Its safer hitting with the front of your helmet than the top of your helmet as far as neck injuries and concussions. I understand it. Ill try to do my best to keep my head up.

The NFL has enlisted the help of coaches, some of whom attended a player-safety summit at the league office in New York in May. Head coaches narrated a set of videos about the new rule distributed to teams. But many have remained confounded. Philadelphia Eagles players complained after officials made their annual visit to the teams training camp late last month that the officials could not explain the new rule clearly to them.

Some observers speculate that the new rule will be called often during the preseason, but the penalties will come with less frequency during the regular season.

I think in the preseason theyll probably address it and people will adjust to it, Johnson said last week. Well probably see some flags. I think in the regular season, people will probably get used to it. Just like anything, its adjustments. . . . I guess well see when they implement the rule, and see how the game is being played and see how the hits are being made and how close theyre calling that type of stuff.

But McKay said he doesnt expect officials to approach preseason application of the rule any differently than regular season application of it.

I think the enforcement will be even, McKay said. A lot of times when you have a point of emphasis for the officials, you might see something like that. . . . This is different than that. This is a new rule. I do think for the officials – where your eyes are and what youre watching – its not like its easy. But I think theyll adjust and handle it well.

McKay was speaking as he traveled back to the Falcons camp on the morning after the Hall of Fame Game. He hadnt been able to watch the game on TV because of a commitment. But hed been on an email chain about it soon afterward. No one needed to tell him what the reaction would be.

We understand what change means, McKay said. Change leads to some uneasiness, some complaints. But I think well be fine. People underestimate the ability of our coaches and our players to adjust. They will adjust.

Colvin agreed that players will adapt. After all, they arent being given a choice.

I dont have to change much, Colvin said. Ive been kind of taught that my whole career, to tackle with your head up. I like to shoot the legs, shoot the thighs, whatever that is, and make the tackle. . . . Guys have been playing football their whole lives. Theyre here for a reason. If they couldnt tackle, Im pretty sure they wouldnt be playing defense. Unfortunately thats just what the rules are. We have to adjust. If you cant do it, then Im sure theyll find somebody that can.